Sacrificial anode assembly

ABSTRACT

A sacrificial anode assembly for cathodically protecting and/or passivating a metal section, comprising: (a) a cell, which has an anode and a cathode arranged so as to not be in electronic contact with each other but so as to be in ionic contact with each other such that current can flow between the anode and the cathode; (b) a connector attached to the anode of the cell for electrically connecting the anode to the metal section to be cathodically protected; and (c) a sacrificial anode electrically connected in series with the cathode of the cell; wherein the cell is otherwise isolated from the environment such that current can only flow into and out of the cell via the sacrificial anode and the connector. The invention also provides a method of cathodically protecting metal in which such a sacrificial anode assembly is cathodically attached to the metal via the connector of the assembly, and a reinforced concrete structure wherein some or all of the reinforcement is cathodically protected by such a method.A sacrificial anode assembly for cathodically protecting and/or passivating a metal section, includes a cell with an anode and a cathode, a connector attached to the anode of the cell for electrically connecting the anode to the metal section to be cathodically protected; and a sacrificial anode electrically connected in series with the cathode of the cell. The cell is otherwise isolated from the environment such that current can only flow into and out of the cell via the sacrificial anode and the connector. A method of cathodically protecting steel in concrete in which such the sacrificial anode assembly is connected to the steel in an initial step of passivation using a higher current and when the first step is terminated the sacrificial anode alone continues to provide protection.

This application is the US national phase of international applicationPCT/GB2005/001651 filed 29 Apr. 2005 which designated the U.S. andclaims benefit of GB 0409521.2, dated 29 Apr. 2004, the entire contentof which is hereby incorporated by reference.

The present invention relates to sacrificial anode assemblies suitablefor use in the sacrificial cathodic protection of steel reinforcementsin concrete, to methods of sacrificial cathodic protection and toreinforced concrete structures wherein the reinforcement is protected bysacrificial cathodic protection.

BACKGROUND OF THE INVENTION

The cathodic protection of metal sections of structures is well known.This technique provides corrosion protection for the metal section bythe formation of an electrical circuit that results in the metal sectionacting as a cathode and therefore oxidation of the metal does not occur.

One such known type of system for cathodic protection is the impressedcurrent system, which makes use of an external power supply, eithermains or battery, to apply current to the metal section to be protectedso as to make it cathodic. These systems generally require complexcircuits to apply the current appropriately and control systems tocontrol the application of the current. Furthermore, those that aresupplied with mains power clearly can encounter difficulties with powersupply problems such as power surges and power cuts, whilst thosepowered by battery have to overcome the issue of locating the battery atan appropriate position, which both allows the battery to functioncorrectly and supports the weight of the battery.

Often, therefore, such impressed current systems have a battery securedto the exterior of the structure containing the metal sections to beprotected, which clearly adversely affects the look of the structure.

Other systems for cathodic protection, which avoid the need for bulky orcomplex components make use of a sacrificial anode coupled to the metalsection. The sacrificial anode is a more reactive metal than the metalof the metal section and therefore it corrodes in preference to themetal section, and thus the metal section remains intact.

This technique is commonly used in the protection of the steelreinforcements in concrete, by electrically connecting the steel to asacrificial anode, with the circuit being completed by electrolyte inthe pores of the concrete. Protection of the steel reinforcements is inparticular required when chloride ions are present at significantconcentrations in the concrete, and therefore cathodic protection iswidely used in relation to concrete structures in locations which areexposed to salt from road de-icing or from marine environments.

A problem associated with such cathodic protection arises from the factthat it is the voltage between the sacrificial anode and the metalsection that drives current through the electrolyte between thesecomponents. This voltage is limited by the natural potential differencethat exists between the metal section and the sacrificial anode.Accordingly, the higher the resistance of the electrolyte, the lower thecurrent flow is across the electrolyte between a given metal section andsacrificial anode, and hence the application of sacrificial cathodicprotection is restricted.

Accordingly, there is a need for a sacrificial anode assembly that cangive rise to a voltage between itself and the metal section greater thanthe natural potential difference that exists between the metal sectionand the material of the sacrificial anode.

SUMMARY OF THE INVENTION

The present invention provides, in a first aspect, a sacrificial anodeassembly for cathodically protecting and/or passivating a metal section,comprising a cell, which has an anode and a cathode arranged so as tonot be in electronic contact with each other but so as to be in ioniccontact with each other such that current can flow between the anode andthe cathode, wherein the anode of the cell is attached to a connectorfor electrically connecting the anode to the metal section to becathodically protected, and the cathode of the cell is electricallyconnected in series with a sacrificial anode, but the cell is otherwiseisolated from the environment such that current can only flow into andout of the cell via the sacrificial anode and the connector.

When such an assembly is connected to a metal section to be cathodicallyprotected, for example a steel section in concrete, the potentialdifference between the metal section and the sacrificial anode isgreater than the natural potential difference between the metal sectionand the sacrificial anode, and therefore a useful level of current flowcan be achieved even in circuits with high resistance. Accordingly, thesacrificial anode assembly can be used to provide sacrificial cathodicprotection of a metal section in locations whereby sacrificial cathodicprotection was not previously able to be applied at a useful level dueto the circuit between the metal section and the sacrificial anode beingcompleted by a material, such as an electrolyte, of high resistance.

Further, as the potential difference between the metal section and thesacrificial anode is greater than the natural potential differencebetween the metal section and the sacrificial anode, it is possible tohave increased spacing between anodes where a multiplicity ofsacrificial anode assemblies are deployed in a structure. This of coursereduces the total number of assemblies required in a given structure.

In addition, the assembly of the present invention produces a highinitial current. This is in particular useful as it allows the assemblyto be used to passivate metals, such as steel, which metals may be in anactive corrosion state or may be in new concrete.

Furthermore, the anode assembly of the present invention may suitably belocated in a concrete or other structure that includes a metal sectionrequiring cathodic protection, or may be encased in a material identicalor similar to that of the structure and this encased assembly may thenbe secured to the exterior of the structure. The look of the structurecan therefore be maintained, as no components dissimilar in appearanceto the structure itself are present on the exterior of the structure.

When the cell of the assembly of the present invention ultimatelybecomes depleted, the sacrificial element may still remain active andthus continue to provide cathodic protection.

The sacrificial anode and the cell may be connected together so as toform a single unit; in particular the sacrificial anode assembly may bea single unit. This is advantageous in that it reduces the complexity ofthe product and makes it easier to embed the assembly in the structurethat includes the metal section to be protected or in a materialidentical or similar to that of the structure.

In particular, the sacrificial anode may be located in the assembly suchthat it is adjacent to the cell. The sacrificial anode may be of a shapeand size corresponding with the shape of at least part of the cell, suchthat it fits alongside at least part of the cell. In a preferredembodiment the sacrificial anode forms a container within which the cellis located.

The sacrificial anode may be directly connected to the cathode of thecell, being in direct contact with the cathode of the cell, or may beindirectly connected to the cathode of the cell. In a preferredembodiment, the sacrificial anode is indirectly connected to the cathodeof the cell via an electronically conductive separator. This isadvantageous because it assists in preventing the direct corrosion ofthe sacrificial anode at its contact with the cathode of the cell. Forexample, a layer of a metal, such as a layer of plated copper or nickel,may be located between the sacrificial anode and the cathode of the cellso as to allow electronic conduction between these components but toprevent direct contact between these components.

The sacrificial anode must clearly have a more negative standardelectrode potential than the metal to be cathodically protected by thesacrificial anode assembly. Accordingly, when the sacrificial anodeassembly is for use in reinforced concrete, the sacrificial anode musthave a more negative standard electrode potential than steel. Examplesof suitable metals are zinc, aluminium, cadmium and magnesium andexamples of suitable alloys are zinc alloys, aluminium alloys, cadmiumalloys and magnesium alloys. The sacrificial anode may suitably beprovided in the form of cast metal/alloy, compressed powder, fibres orfoil.

The connector for electrically connecting the anode to the metal sectionto be cathodically protected may be any suitable electrical connector,such as a connector known in the art for use with sacrificial anodes. Inparticular the connector may be steel, galvanised steel or brass, andthe connector may suitably be in the form of a wire; preferably theconnector is galvanised steel wire.

The cell may be any conventional electrochemical cell. In particular,the cell may comprise an anode which is any suitable material and acathode which is any suitable material, provided of course that theanode has a more negative standard electrode potential than the cathode.Suitable materials for the anode include metals such as zinc, aluminium,cadmium, lithium and magnesium and alloys such as zinc alloys, aluminiumalloys, cadmium alloys and magnesium alloys. Suitable materials for thecathode include metal oxides such as oxides of manganese, iron, copper,silver and lead, and mixtures of metal oxides with carbon, for examplemixtures of manganese dioxide and carbon. The anode and the cathode mayeach be provided in any suitable form, and may be provided in the sameform or in different forms, for example they may each be provided as asolid element, such as in the form of a cast metal/alloy, compressedpowder, fibres or foil, or may be provided in loose powdered form.

It is preferred that, as in conventional cells, the anode is in contactwith an electrolyte. When the anode is in loose powdered form, thispowder may be suspended in the electrolyte. The electrolyte may be anyknown electrolyte, such as potassium hydroxide, lithium hydroxide orammonium chloride. The electrolyte may contain additional agents, inparticular it may contain compounds to inhibit hydrogen discharge fromthe anode, for example when the anode is zinc the electrolyte maycontain zinc oxide.

The anode and the cathode are arranged so as to not be in electroniccontact with each other but to be in ionic contact with each other suchthat current can flow from the anode to the cathode. In this respect itis preferred that, as in conventional cells, the anode and the cathodeare connected via an electrolyte. Suitably, therefore, an electrolyte isprovided between the anode and the cathode, to allow ionic current toflow between the anode and the cathode.

The cell may be provided with a porous separator located between thecathode and the anode, which consequently prevents direct contactbetween the anode and the cathode. This is in particular useful inassemblies of the present invention whereby the anode is provided inloose powdered form, and more particularly when this powder is suspendedin the electrolyte.

The cell in the assembly is isolated from the environment, other than tothe extent that attachment to the connector and the sacrificial anodemakes necessary; this may be achieved by the use of any suitableisolating means around the cell. This isolation is, in particular,beneficial as it ensures that electrolyte in the environment does notcome into contact with the cell. The cell may be isolated in this way byone isolating means or more than one isolating means which togetherachieve the necessary isolation. The isolating means clearly must beelectrically insulating material, so that current will not flow throughit, such as silicone-based material.

As one of the permitted electrical connections of the cell is anelectrical connection to the sacrificial anode, the amount of isolatingmeans required can be reduced by increasing the area of the exterior ofthe cell located adjacent the sacrificial anode. Accordingly, in apreferred embodiment the sacrificial anode is in the shape of acontainer and the cell is located in the container, for example thesacrificial anode may be in the shape of a can, i.e. having a circularbase and a wall extending upwards from the circumference of the base soas to define a cavity, and the cell is located in this can. Theremaining areas of the cell that are not covered by the sacrificialanode and that are not covered by their contact with the connector areof course isolated from the environment by isolating means.

It is preferred that the quantities of the anode and cathode materialsutilised in the assembly are such that they will each deliver the samequantity of charge during the life of the assembly, as this clearlymaximises the efficiency of this system.

The anode assembly may be surrounded by an encapsulating material, suchas a porous matrix. In particularly, the assembly may have a suitableencapsulating material pre-cast around it before use. Alternatively, theencapsulating material may be provided after the assembly is located atits intended position, for example after the assembly has been locatedin a cavity in a concrete structure; in this case a suitableencapsulating material may be deployed to embed the assembly.

The encapsulating material may suitably be such that it can maintain theactivity of the sacrificial anode casing, absorb any expansive forcesgenerated by expansive corrosion products, and/or minimise the risk ofdirect contact between the conductor and the sacrificial anode, whichwould discharge the internal cell in the anode assembly. Theencapsulating material may, for example, be a mortar, such as acementitious mortar.

Preferably the anode assembly is surrounded by an encapsulating materialcontaining activators to ensure continued corrosion of the sacrificialanode, for example an electrolyte that in solution has a pH sufficientlyhigh for corrosion of the sacrificial anode to occur and for passivefilm formation on the sacrificial anode to be avoided when the anodeassembly is cathodically connected to the material to be cathodicallyprotected by the anode assembly. In particular, the encapsulatingmaterial may comprise a reservoir of alkali such as lithium hydroxide orpotassium hydroxide, or other suitable activators known in the art, suchas humectants. The encapsulating material is preferably a highlyalkaline mortar, such as those known in the art as being of use forsurrounding sacrificial zinc, for example a mortar comprising lithiumhydroxide or potassium hydroxide and having a pH of from 12 to 14.

The mortar may suitably be rapid hardening cement; this is particularlyof use in embodiments whereby the encapsulating material is to bepre-cast. For example, the mortar may be a calcium sulphoaluminate. Themortar may alternatively be a Portland cement mortar with a water/cementratio of 0.6 or greater containing additional lithium hydroxide orpotassium hydroxide, such as those mortars discussed in U.S. Pat. No.6,022,469.

In a second aspect, the present invention provides a method ofcathodically protecting metal in which a sacrificial anode assembly inaccordance with the first aspect of the present invention iscathodically attached to the metal via the connector of the assembly. Inparticular, a method of cathodically protecting steel reinforcement inconcrete is provided, in which a sacrificial anode assembly inaccordance with the first aspect of the present invention iscathodically attached to the steel.

In a third aspect, the present invention provides a reinforced concretestructure wherein some or all of the reinforcement is cathodicallyprotected by the method of the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described in the following examples,with reference to the drawings in which:

FIG. 1a shows a cross section through a sacrificial anode assembly inaccordance with the invention;

FIG. 1b shows a section A-A through the sacrificial anode assembly asshown in FIG. 1a;

FIG. 2 shows a sacrificial anode assembly of the present inventionconnected to steel in a test arrangement;

FIG. 3 is a graph showing the drive voltage and current density of thesacrificial anode assembly as shown in FIG. 3; and

FIG. 4 shows the potential and current density for the protected steelas connected to the sacrificial anode assembly in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Example 1

FIG. 1 shows a sacrificial anode assembly 1 for cathodically protectinga metal section. The assembly comprises a cell, which has an anode 2 anda cathode 3. The cathode 3 is a manganese dioxide/carbon mixture and isin the shape of a can, having a circular base and a wall extendingupwards from the circumference of the base, so as to define a cavity.The anode 2 is a solid zinc anode of cylindrical shape, with the solidzinc being cast metal, compressed powder, fibres or foil. The anode 2 islocated centrally within the cavity defined by the can shaped cathode 3and is in contact with electrolyte 4 present in the cavity defined bythe can shaped cathode 3, which maintains the activity of the anode. Theelectrolyte 4 is suitably potassium hydroxide, and may contain otheragents such as zinc oxide to inhibit hydrogen discharge from the zinc. Aporous separator 5, which is can shaped, is located inside the cavity 3adefined by the cathode 3, adjacent to the cathode 3. Accordingly, anode2 and cathode 3 are not in electronic contact with each other, but areionically connected via the electrolyte 4 and porous separator 5 suchthat current can flow between the anode 2 and the cathode 3.

The anode 2 is attached to a connector 6 for electrically connecting theanode 2 to the metal section to be cathodically protected. The connector6 is suitably galvanised steel. The cathode 3 of the cell iselectrically connected in series with a sacrificial anode 7. Sacrificialanode 7 is solid zinc and is can shaped, with the solid zinc being castmetal, compressed powder, fibres or foil. The cell is located inside thecavity defined by the can shaped sacrificial anode 7. A layer ofelectrically insulating material 8 is located across the top of theassembly to isolate the cell from the external environment andaccordingly current can only flow into and out of the cell via thesacrificial anode 7 and the connector 6.

The sacrificial anode assembly 1 may subsequently be surrounded by aporous matrix; in particular a cementitious mortar such as a calciumsulphoaluminate may be pre-cast around the assembly 1 before use. Thematrix may also suitably comprise a reservoir of alkali such as lithiumhydroxide.

The sacrificial anode assembly 1 may be utilised by being located in aconcrete environment and connecting the conductor 6 to a steel bar alsolocated in the concrete. Current is accordingly driven through thecircuit comprising the anode assembly 1, the steel and the electrolytein the concrete, by the voltage across the cell and the voltage betweenthe sacrificial anode 7 and the steel, which two voltages combineadditatively. The reactions that occur at the metal/electrolyteinterfaces result in the corrosion of the zinc sacrificial anode 7 andthe protection of the steel.

Example 2

FIG. 2 shows a sacrificial anode assembly 11 connected to a 20 mmdiameter mild steel bar 12 in a 100 mm concrete cube 13 consisting of350 kg/m³ ordinary Portland cement concrete contaminated with 3%chloride ion by weight of cement.

The sacrificial anode assembly 11 comprises a cell, which is an AA sizeDuracell battery, and a sacrificial anode, which is a sheet of pure zincfolded to produce a zinc can around the cell. This zinc is folded so asto contact the positive terminal of the cell, and a conductor 14 issoldered to the negative terminal of the cell. A silicone-based sealantis located over the negative and positive cell terminals so as toinsulate them from the environment.

Prior to placing the sacrificial anode assembly 11 in the concrete cube,potentials were measured using a digital multimeter with an inputimpedance of 10 Mohm, which showed that the potential between theexternal zinc casing and a steel bar in moist chloride contaminated sandwas 520 mV and the potential between the conductor and the steel was2110 mV. This suggests that the sacrificial anode assembly 11 would have1590 mV of additional driving voltage over that of a conventionalsacrificial anode to drive current through the electrolyte between theanode and the protected steel.

As shown in FIG. 2, the circuit from the sacrificial anode assembly 11through the electrolyte in the concrete cube 13 to the steel bar 12 wascompleted by copper core electric cables 15, with a 10 kOhm resistor 16and a circuit breaker 17 also being included in the circuit. The drivevoltage between the anode and the steel was monitored across monitoringpoints 18 while the current flowing was determined by measuring thevoltage across the 10 kOhm resistor at monitoring points 19. A saturatedcalomel reference electrode (SCE) 20 was installed to facilitate theindependent determination of the steel potential across monitoringpoints 21.

The drive voltage, sacrificial cathodic current and steel potential werelogged at regular intervals. The drive voltage and sacrificial cathodiccurrent expressed relative to the anode surface area are shown in FIG.3. The anode-steel drive voltage was approximately 2.2 to 2.4 volts inthe open circuit condition (circuit breaker open) and fell to 1.5 to 1.8volts when current was been drawn.

The steel potential and sacrificial cathodic current expressed relativeto the steel surface area are shown in FIG. 4. The initial steelpotential varied between −410 and −440 mV on the SCE scale. This variedwith the moisture content of the concrete at the point of contactbetween the SCE and the concrete. This negative potential reflects theaggressive nature of the chloride contaminated concrete towards thesteel. The steel current density varied between 25 and 30 mA/m².

The steel potential decay following the interruption of the current(circuit breaker open) was approximately 100 mV, indicating that steelprotection is being achieved. This also means that, of the 1.5 to 1.8volts anode-steel drive voltage, more than 1.4 volts would be availableto overcome the circuit resistance to current flow. This issignificantly more voltage than could be provided by a sacrificial anodeas currently available to overcome circuit resistance to current flow.

It is therefore clear that in high resistivity environments, i.e. wherethe circuit resistance to current flow presented by the conditions ishigh, the sacrificial anode assembly of the present invention has asignificant advantage over the more traditional sacrificial anodescurrently available.

The invention claimed is:
 1. A sacrificial anode assembly forcathodically protecting and/or passivating a metal section, comprising:a cell, which has an anode and a cathode arranged so as to not be inelectronic contact with each other but so as to be in ionic contact witheach other such that current can flow between the anode and the cathode;a connector attached to the anode of the cell for electricallyconnecting the anode to the metal section to be cathodically protected;and a sacrificial anode electrically connected in series with thecathode of the cell; wherein there are provided one or more isolatingelements which prevent communication of ionic current from the cell tothe environment such that current can only flow between the cathode ofthe cell and the sacrificial anode and between the anode of the cell andthe connector; and wherein the sacrificial anode and the cell areconnected together so as to form a single unit such that the sacrificialanode is electrically connected in series with the cathode of the cell.2. An assembly according to claim 1, wherein the sacrificial anode is ofa shape and size corresponding with the shape of at least part of thecell, such that it fits alongside at least part of the cell.
 3. Anassembly according to claim 1, wherein the sacrificial anode forms acontainer within which the cell is at least partly located.
 4. Anassembly according to claim 1, wherein the sacrificial anode isindirectly connected to the cathode of the cell through anelectronically conductive separator.
 5. An assembly according to claim4, wherein a layer of a metal is located between the sacrificial anodeand the cathode of the cell so as to allow electronic conduction betweenthese components but to prevent direct contact between these components.6. An assembly according to claim 1, wherein the sacrificial anode iszinc, aluminum, cadmium or magnesium, or an alloy of one or more ofthese metals.
 7. An assembly according to claim 1, wherein the cell isprovided with a porous separator located between the cathode and theanode, which prevents direct contact between the anode and the cathode.8. An assembly according to claim 1, wherein the sacrificial anode formsa container and the cell is located at least partly in the container. 9.An assembly according to claim 8 wherein the sacrificial anode is in theshape of a generally cylindrical can and the cell is at least partlylocated in this can.
 10. An assembly according to claim 1 which is atleast partly surrounded by an encapsulating material.
 11. An assemblyaccording to claim 10 wherein the encapsulating material is a porousmatrix.
 12. An assembly according to claim 11 wherein the porous matrixcomprises a cementitious mortar.
 13. An assembly according to claim 12wherein the porous matrix comprises a mortar having a pH greater than12.
 14. An assembly according to claim 10 wherein the encapsulatingmaterial contains at least one activator to ensure continued corrosionof the sacrificial anode.
 15. An assembly according to claim 14 whereinthe activator comprises a humectant.
 16. A method of cathodicallyprotecting a metal section steel in an ionically conductive concrete ormortar covering material comprising: providing a sacrificial anode;generating a voltage between two connections of a power supply such thatcurrent can flow between the negative connection and the positiveconnection; in a first protection step, electrically connecting one ofthe connections of the power supply to the metal section steel to becathodically protected and electrically connecting the sacrificial anodein series with the other connection of the power supply such that thevoltage generated by the power supply is added to the voltage generatedbetween the sacrificial anode and the metal steel to produce a voltagegreater than the galvanic voltage generated between the sacrificialanode and the metal section steel alone; wherein the power supply isotherwise isolated from the environment such that current can only flowinto and out of the power supply via the sacrificial anode and theconnector; and, in a second protection step, the voltage generated bythe power supply is no longer present and a current flows between thesacrificial anode and the metal steel to continue protecting and/orpassivating the metal section steel, where the current is generatedsolely by the galvanic voltage between the sacrificial anode and themetal steel.
 17. The method according to claim 16 wherein thesacrificial anode and the power supply are connected together so as toform a single unit.
 18. The method according to claim 17 wherein thesacrificial anode is of a shape and size corresponding with the shape ofat least part of the power supply, such that it fits alongside at leastpart of the anode and cathode.
 19. The method according to claim 16wherein the sacrificial anode forms a container within which the powersupply is at least partly located.
 20. The method according to claim 16including surrounding the sacrificial anode by an encapsulating materialof a porous matrix.
 21. The method according to claim 20 wherein theporous matrix comprises a cementitious mortar.
 22. The method accordingto claim 20 including surrounding the sacrificial anode by anencapsulating material wherein the porous matrix comprises a mortarhaving encapsulating material has a pH greater than
 12. 23. The methodaccording to claim 20 wherein the encapsulating material is pre-castaround the anode.
 24. The method according to claim 20 wherein theencapsulating material is provided after as the sacrificial anode islocated at its intended position in the concrete or mortar material. 25.The method according to claim 16 wherein the sacrificial anode isactivated to ensure continued corrosion of the sacrificial anode. 26.The method according to claim 16 wherein the power supply comprises anelectrolytic cell.
 27. The method according to claim 16 wherein theionically conductive material is a concrete or mortar material incontact with which the metal steel is a steel reinforcing member.
 28. Asacrificial anode assembly for cathodically protecting and/orpassivating a metal section within an ionically conductive concrete ormortar covering material, comprising: a cell, which has an anode and acathode with an electrolyte therebetween such that current can flowbetween the anode and the cathode; a connector attached to the anode ofthe cell for electrically connecting the anode to the metal section tobe cathodically protected; and sacrificial anode material electricallyconnected with the cathode of the cell; wherein there are provided oneor more isolating elements which prevent communication of ionic currentfrom the cell to the environment such that current can only flow betweenthe cathode of the cell and the sacrificial anode and between the anodeof the cell and the connector; wherein the sacrificial anode and thecell are connected together so as to form a single unit such that thesacrificial anode is electrically connected in series with the cathodeof the cell; wherein the assembly comprises a container containing atleast part of the anode, the electrolyte and the cathode of the cell;and wherein the sacrificial anode material forms at least part of anouter surface of the container.
 29. An assembly according to claim 28,wherein the sacrificial anode is zinc, aluminum, cadmium or magnesium,or an alloy of one or more of these metals.
 30. An assembly according toclaim 28 wherein the cell and the container are generally cylindrical.31. An assembly according to claim 28 wherein the container is at leastpartly surrounded by an encapsulating material.
 32. An assemblyaccording to claim 31 wherein the encapsulating material is a porousmatrix.
 33. An assembly according to claim 31 wherein the encapsulatingmaterial comprises a cementitious mortar.
 34. An assembly according toclaim 33 wherein the encapsulating material has a pH greater than 12.35. An assembly according to claim 31 wherein the encapsulating materialcontains at least one activator to ensure continued corrosion of thesacrificial anode.
 36. An assembly according to claim 35 wherein theactivator comprises a humectant.
 37. A method of cathodically protectingsteel in an ionically conductive concrete or mortar covering materialcomprising: providing a sacrificial anode; generating a voltage betweentwo connections of a power supply such that current can flow between thenegative connection and the positive connection; in a first protectionstep, electrically connecting one of the connections of the power supplyto the steel to be cathodically protected and electrically connectingthe sacrificial anode in series with the other connection of the powersupply such that the voltage generated by the power supply is added tothe voltage generated between the sacrificial anode and the steel toproduce a voltage greater than the galvanic voltage generated betweenthe sacrificial anode and the steel alone which passivates the steel;wherein the power supply is otherwise isolated from the environment suchthat current can only flow into and out of the power supply via thesacrificial anode and the connector; and, in a second protection step,subsequent to completion of the first step, the voltage generated by thepower supply is no longer present and a current flows between thesacrificial anode and the steel to continue protecting and/orpassivating the steel, where the current is generated solely by thegalvanic voltage between the sacrificial anode and the steel.
 38. Themethod according to claim 37 wherein a porous material is provided atthe sacrificial anode so as to provide pores that absorb expansiveforces generated by expansive corrosion products.
 39. The methodaccording to claim 37 including providing at least one activator whichensures continued corrosion of the sacrificial anode.
 40. The methodaccording to claim 39 wherein said at least one activator provides a pHin the encapsulating material sufficiently high for corrosion of thesacrificial anode to occur and for passive film formation on thesacrificial anode to be avoided.
 41. The method according to claim 39wherein said at least one activator provides a pH in the encapsulatingmaterial greater than
 12. 42. The method according to claim 39 whereinsaid at least one activator is provided in a porous material at thesacrificial anode.
 43. The method according to claim 37 wherein thesacrificial anode is formed of zinc or zinc alloy.
 44. The methodaccording to claim 37 wherein an encapsulating material is pre-castaround the sacrificial anode.
 45. The method according to claim 37wherein an encapsulating material is provided around the sacrificialanode as the sacrificial anode is located at its intended position inthe concrete or mortar covering material.